Fix filename reference in configmaps-secrets.md

Corrected the filename reference from 'postgres-svc.yaml' to 'postgres-service.yaml'.

Author: kierenevans

configmaps-secrets.md

@@ -173,7 +173,7 @@ We have already created the database part of the application, with a deployment
 > :bulb: This is not a good practice, as we do not want to store these values in version control.
 > We will fix this in the next steps.
 
-- Look at the service file in `postgres-svc.yaml`.
+- Look at the service file in `postgres-service.yaml`.
   It provides a service for the database, so that the backend can connect to it.
 
 - Apply the whole folder with `kubectl apply -f .`